1. Field of the Invention
The present invention relates to a hydraulic clamp which serves to fixedly press a member to be clamped, through a clamping means by a hydraulic oil pressure of a hydraulic cylinder.
2. Background of the Prior Art
Means for detachably fixing a member to be clamped to a fixed member, have been known e.g. the one shown in FIG. 33.
In this example, a flange 303 of a cylinder head 302 that is member to be clamped is adapted to be fixed to a screw cylinder 301 as a fixed member of an injection molding machine by means of a plurality of detachable bolts 304.
This fixing means has an advantage of being simple in construction, but has a disadvantage in that it requires much labor for clamping because the detachable bolts 304 are threadably engaged and tightened manually in threaded holes of the screw cylinder 301 whenever the cylinder 302 as a member to be clamped is exchanged.
For eliminating this disadvantage, the inventor of the present invention previously contrived a clamping apparatus which performs a clamping operation automatically through a plurality of hydraulic clamps of the type having retractable clamping means. Construction of a hydraulic clamp of the type having retractable clamping means is known, for example as shown in U.S. Pat. No. 4,504,046 (Date of Patent: Mar. 12, 1985) proposed previously by the inventor of the present invention.
The above-mentioned clamping apparatus has an adapter plate fixed on the leading end surface of a screw cylinder and a plurality of hydraulic cylinders arranged in the peripheral direction of the adapter plate with the respective clamping means thereof facing toward the center side of the adapter plate. At the time of the clamping operation, first of all the clamping means of each hydraulic cylinder is retracted in the front portion of the clamp body and then a cylinder head is placed on the central portion of the adapter plate under such retracted condition of the clamping means. Next, the clamping means is advanced outside the front portion of the clamp body by a hydraulic pressure of the hydraulic cylinder so that the flange of the cylinder head as a passive portion is pressed to the adapter plate by each clamping means.
However, the following disadvantages (a) and (b) are associated with the clamp apparatus:
(a) The whole of the clamp apparatus is large.
Since the respective hydraulic clamps project radially from the clamping position of the member to be clamped, the external size of the clamp apparatus gets large and the whole thereof gets large-sized.
(b) The clamping force per unit area is small.
Since the arrangement pitches of the clamping means in the peripheral direction get necessarily large for preventing the interferences between the neighboring hydraulic clamps and the unclampable range gets large, the clamping force per unit area is small. Therefore, the pressure per unit area exerted to the flange of the member to be clamped gets large and tends to damage and deform the flange.